Estrogen relaxes gastric muscle cells via a nitric oxide- and cyclic guanosine monophosphate-dependent mechanism: A sex-associated differential effect

Risk factors for developing irritable bowel syndrome: systematic umbrella review of reviews

BACKGROUND

Irritable bowel syndrome (IBS) is a debilitating disorder affecting 4-9% of the global population. It is a multifaceted disorder with complex and varied causes. This review aims to consolidate the evidence regarding IBS risk factors by examining existing systematic reviews and meta-analyses, covering potential genetic, immunological, psychological, and dietary causes.

METHODS

Systematic literature searches were conducted in MEDLINE, Embase and Cochrane library databases. Study selection and data extraction were conducted independently by four authors, with discrepancies resolved by consensus with a senior author. Systematic reviews examining risk factors of IBS development were eligible for review. Results were narratively synthesized. Quality of reviews were analysed using AMSTAR 2, and evidence were appraised using GRADE methodology.

RESULTS

A total of 69 systematic reviews were included in this study. Most reviews were of "critically low" quality, while the remaining were "low" quality. Common shortcomings included the absence of a list of excluded studies with justifications for their exclusion and inadequate consideration of the risk of bias in individual studies. Eight major categories of risk factors for IBS identified were as follows: dietary, genetic, environmental, psychological, gut microbiome, socio-economic, physiological, and pathological, albeit overlaps exist. The most frequently reported risk factors for IBS development were female gender and anxiety disorders, with overall GRADE evaluation of "low"; depression and gastroenteritis, with overall GRADE evaluation of "moderate".

CONCLUSIONS

Clinical practice should prioritize recognition of these risk factors. Future reviews should improve their reporting of results based on the PRISMA guidelines, to enhance the quality of research in this field.

PROTOCOL REGISTRATION

PROSPERO CRD42023493739.

Plasticity of colonic enteric nervous system following spinal cord injury in male and female rats

BACKGROUND

Neurogenic bowel is a dysmotility disorder following spinal cord injury (SCI) that negatively impacts quality of life, social integration, and physical health. Colonic transit is directly modulated by the enteric nervous system. Interstitial Cells of Cajal (ICC) distributed throughout the small intestine and colon serve as specialized pacemaker cells, generating rhythmic electrical slow waves within intestinal smooth muscle, or serve as an interface between smooth muscle cells and enteric motor neurons of the myenteric plexus. Interstitial Cells of Cajal loss has been reported for other preclinical models of dysmotility, and our previous experimental SCI study provided evidence of reduced excitatory and inhibitory enteric neuronal count and smooth muscle neural control.

METHODS

Immunohistochemistry for the ICC-specific marker c-Kit was utilized to examine neuromuscular remodeling of the distal colon in male and female rats with experimental SCI.

KEY RESULTS

Myenteric plexus ICC (ICC-MP) exhibited increased cell counts 3 days following SCI in male rats, but did not significantly increase in females until 3 weeks after SCI. On average, ICC-MP total primary arborization length increased significantly in male rats at 3-day, 3-week, and 6-week time points, whereas in females, this increase occurred most frequently at 6 weeks post-SCI. Conversely, circular muscle ICC (ICC-CM) did not demonstrate post-SCI changes.

CONCLUSIONS AND INFERENCES

These data demonstrate resiliency of the ICC-MP in neurogenic bowel following SCI, unlike seen in other related disease states. This plasticity underscores the need to further understand neuromuscular changes driving colonic dysmotility after SCI in order to advance therapeutic targets for neurogenic bowel treatment.

A systematic review and meta-analysis of the correlation between polycystic ovary syndrome and irritable bowel syndrome

BACKGROUND

Research on the prevalence of irritable bowel syndrome (IBS) among polycystic ovary syndrome (PCOS) patients has gained significant momentum over the years. However, it remains unclear whether PCOS is related to a higher prevalence of IBS. The objective of this systematic review and meta-analysis was to fully study IBS correlation with PCOS.

METHODS

From inception until October 16th, 2022, all observational studies documenting IBS prevalence in PCOS patients were collected from the China national knowledge infrastructure(CNKI), China Science and Technology Journal Database(VIP), Wanfang database, PubMed, Embase, Web of Science, and Cochrane databases. The quality of case-control studies was assessed with Newcastle-Ottawa Scale. Review Manager 5.3 was used to determine the pooled odds ratio (OR) and 95% confidence interval (CI).

RESULTS

5 case-control studies involving 1268 individuals and one cross-sectional study involving 291 participants were included in our qualitative analysis. The quantitative analysis was conducted based on five case-control studies. Four case-control studies involving 1063 participants showed a higher prevalence of IBS in PCOS This meta-analysis revealed an almost twice higher risk of IBS in comparison with controls (OR = 2.23, 95%CI:1.58-3.14, p < 0.001; I²=41%, p = 0.150). Four sensitivity analyses validated the consistency of the aggregated findings.

CONCLUSION

This meta-analysis and systematic review demonstrated a significant association between PCOS and increased odds of IBS. However, more high-quality and well-controlled research is essential to increase the robustness of our conclusions.

Quercetin relaxes human gastric smooth muscles directly through ATP-sensitive potassium channels and not depending on the nitric oxide pathway

BACKGROUND

Quercetin has recently become a remarkably popular subject of research due to its broad beneficial pharmacological properties. The goal of our study was to observe its effects on contractility of human gastric smooth muscles in reference to the NO pathway and direct influence of potassium channels.

METHODS

Tissues were obtained from patients undergoing sleeve gastrectomy due to morbid obesity (n = 10 aged 24-56; BMI 47.16 ± 1.84). The following parameters were evaluated in the recordings: area under the curve (AUC), average baseline muscle tone, and relative change in muscle contraction.

KEY RESULTS

Quercetin induced noticeable, dose-dependent relaxation of the carbachol treated gastric strips. The substantial effect was noted at concentrations higher than 10^-7  mol/L and maximal at 10^-4  mol/L (81.82 ± 3.32%; n = 10; p < 0.0001) of the control. Neither NOS blockers nor guanylyl cyclase blockers had inhibitory effects on the relaxation of strips induced by examined polyphenol. Glibenclamide inhibited the relaxing effect of quercetin, significant at concentrations higher than 5⋅10^-5  mol/L. Preincubation with charybdotoxin or apamin extended the relaxing effect of quercetin (from 10^-6  mol/L). Tamoxifen, in turn, significantly increased muscle relaxation at all quercetin concentrations.

CONCLUSIONS & INFERENCES

In conclusion, the current study was the first to show that quercetin-induced relaxation of human gastric smooth muscle occurs directly through K⁺_ATP channels and independently to NO pathways. The present results suggest that quercetin is a potential nutraceutical in the treatment of functional gastrointestinal dyspepsia and other minor gastric muscle motility disturbance.

Loss of PKGIβ/IRAG1 Signaling Causes Anemia-Associated Splenomegaly

Inositol 1,4,5-triphosphate receptor-associated cGMP kinase substrate 1 (IRAG1) is a substrate protein of the NO/cGMP-signaling pathway and forms a ternary complex with the cGMP-dependent protein kinase Iβ (PKGIβ) and the inositol triphosphate receptor I (IP₃R-I). Functional studies about IRAG1 exhibited that IRAG1 is specifically phosphorylated by the PKGIβ, regulating cGMP-mediated IP₃-dependent Ca²⁺-release. IRAG1 is widely distributed in murine tissues, e.g., in large amounts in smooth muscle-containing tissues and platelets, but also in lower amounts, e.g., in the spleen. The NO/cGMP/PKGI signaling pathway is important in several organ systems. A loss of PKGI causes gastrointestinal disorders, anemia and splenomegaly. Due to the similar tissue distribution of the PKGIβ to IRAG1, we investigated the pathophysiological functions of IRAG1 in this context. Global IRAG1-KO mice developed gastrointestinal bleeding, anemia-associated splenomegaly and iron deficiency. Additionally, Irag1-deficiency altered the protein levels of some cGMP/PKGI signaling proteins—particularly a strong decrease in the PKGIβ—in the colon, spleen and stomach but did not change mRNA-expression of the corresponding genes. The present work showed that a loss of IRAG1 and the PKGIβ/IRAG1 signaling has a crucial function in the development of gastrointestinal disorders and anemia-associated splenomegaly. Furthermore, global Irag1-deficient mice are possible in vivo model to investigate PKGIβ protein functions.

Mechanistic role of antioxidants in rescuing delayed gastric emptying in high fat diet induced diabetic female mice

Diabetic gastroparesis (DG) exhibits delayed gastric emptying (GE) due to impaired gastric non-adrenergic, non-cholinergic (NANC) relaxation. These defects are due to loss or reduction of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) that causes reduced expression and/or dimerization of neuronal nitric oxide synthase alpha (nNOSα) gene expression and function. We investigated the effect of potent Nrf2 activators (cinnamaldehyde [CNM] & curcumin [CUR]) on GE in obesity-induced diabetic female mice. We fed adult female homozygous Nfe2l2-/- (Nrf2 KO) and wild-type (WT) female mice with either a high-fat diet (HFD) or a normal diet (ND) for a period of 16 weeks. Groups of HFD mice were fed with CUR or CNM either at 6th or 10th week respectively. Our results demonstrate that supplementation of CNM or CUR restored impaired nitrergic relaxation and attenuated delayed GE in HFD fed mice. Supplementation of CNM or CUR normalized altered gastric antrum protein expression of (1) p-ERK/p-JNK/MAPK/p-GSK-3β, (2) BH4 (Cofactor of nNOS) biosynthesis enzyme GCH-1 and the GSH/GSSG ratio, (3) nNOSα protein & dimerization and soluble guanylate cyclase (sGC), (4) AhR and ER expression, (5) inflammatory cytokines (TNF α, IL-1β, IL-6), (6)TLR-4, as well as (7) reduced oxidative stress markers in WT but not in Nrf2 KO obesity-induced chronic diabetic female mice. Immunoprecipitation experiments revealed an interaction between nNOS and Nrf2 proteins. Our results conclude that Nrf2 activation restores nitrergic-mediated gastric motility and GE by normalizing inflammation and oxidative stress induced by obesity-induced chronic diabetes.

Sex-Bias in Irritable Bowel Syndrome: Linking Steroids to the Gut-Brain Axis

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that is more common in females. Despite its high global incidence, the disease mechanism is still unclear and therapeutic options remain limited. The sexual dimorphism in IBS incidence suggests that sex steroids play a role in disease onset and symptoms severity. This review considers sex steroids and their involvement in IBS symptoms and the underlying disease mechanisms. Estrogens and androgens play important regulatory roles in IBS symptomology, including visceral sensitivity, gut motility and psychological conditions, possibly through modulating the gut-brain axis. Steroids are regulators of hypothalamic-pituitary-adrenal activity and autonomic nervous system function. They also modulate gut microbiota and enteric nervous systems, impacting serotonin and mast cell signaling. Sex steroids also facilitate bidirectional cross-talk between the microbiota and host following bacterial transformation and recycling of steroids by the intestine. The sex-specific interplay between sex steroids and the host provides neuroendocrinology insight into the pathophysiology, epigenetics and treatment of IBS patients.

Role of sex hormones and their receptors on gastric Nrf2 and neuronal nitric oxide synthase function in an experimental hyperglycemia model

BACKGROUND

Gastroparesis, a condition of abnormal gastric emptying, is most commonly observed in diabetic women. To date, the role of ovarian hormones and/or gastric hormone receptors on regulating nitrergic-mediated gastric motility remains inconclusive.

AIM

The purpose of this study is to investigate whether sex hormones/their receptors can attenuate altered Nuclear factor (erythroid-derived 2)-like 2 (Nrf2), neuronal Nitric Oxide Synthase (nNOS) expression and nitrergic relaxation in gastric neuromuscular tissues exposed to in-vitro hyperglycemia (HG).

METHODS

Gastric neuromuscular sections from adult female C57BL/6 J mice were incubated in normoglycemic (NG, 5 mM) or hyperglycemic (30 mM or 50 mM) conditions in the presence or absence of selective estrogen receptor (ER) agonists (ERα /PPT or ERβ: DPN); or non-selective sex hormone receptor antagonists (ER/ICI 182,780, or progesterone receptor (PR)/ RU486) for 48 h. mRNA, protein expression and nitrergic relaxation of circular gastric neuromuscular strips were assessed.

RESULTS

Our findings in HG, compared to NG, demonstrate a significant reduction in ER, Nrf2, and nNOS expression in gastric specimens. In addition, in-vitro treatment with sex hormones and/or their agonists significantly (*p < 0.05) restored Nrf2/nNOSα expression and total nitrite production. Conversely, ER, but not PR, antagonist significantly reduced Nrf2/nNOSα expression and nitrergic relaxation.

CONCLUSIONS

Our data suggest that ER's can regulate nitrergic function by improving Nrf2/nNOS expression in experimental hyperglycemia.

Supplementation of 17β-Estradiol Normalizes Rapid Gastric Emptying by Restoring Impaired Nrf2 and nNOS Function in Obesity-Induced Diabetic Ovariectomized Mice

Gastroparesis (Gp) is a multifactorial condition commonly observed in females and is characterized by delayed or rapid gastric emptying (GE). The role of ovarian hormones on GE in the pathogenesis of obesity induced type 2 diabetes mellitus (T2DM) is completely unknown. The aims of our study are to investigate whether supplementation of 17β-estradiol (E2) or progesterone (P4) restores impaired nuclear factor erythroid 2-related factor 2 (Nrf2, an oxidative stress-responsive transcription factor) and nitric oxide (NO)-mediated gastric motility in ovariectomized (OVX) mice consuming a high-fat diet (HFD, a model of T2DM). Groups of OVX+HFD mice were administered daily subcutaneous doses of either E2 or P4 for 12 weeks. The effects of E2 and P4 on body weight, metabolic homeostasis, solid GE, gastric antrum NO-mediated relaxation, total nitrite levels, neuronal nitric oxide synthase (nNOSα), and its cofactor expression levels were assessed in OVX+HFD mice. HFD exacerbated hyperglycemia and insulinemia while accelerating GE (p < 0.05) in OVX mice. Exogenous E2, but not P4, attenuated rapid gastric emptying and restored gastric nitrergic relaxation, total nitrite levels, nNOSα, and cofactor expression via normalizing Nrf2-Phase II enzymes, inflammatory response, and mitogen-activated protein kinase (MAPK) protein expression in OVX+HFD mice. We conclude that E2 is beneficial in normalizing metabolic homeostasis and gastric emptying in obese, diabetic OVX mice consuming a fat-rich diet.

Hypoganglionosis in the gastric antrum causes delayed gastric emptying

BACKGROUND

Enteric nervous system (ENS) abnormalities have been implicated in delayed gastric emptying but studies exploring potential treatment options are limited by the lack of an experimental animal model. We examined the ENS abnormalities in the mouse stomach associated with aging, developed a novel model of gastroparesis, and established a new approach to measure gastric emptying.

METHODS

A modified gastric emptying assay was developed, validated in nNOS ^-/- mice, and tested in mice at multiple ages. Age-related changes in ENS structure were analyzed by immunohistochemistry. Gastric aganglionosis was generated in Wnt1-iDTR mice using focal administration of diphtheria toxin (DT) into the anterior antral wall.

KEY RESULTS

Older mice (>5 months) exhibit hypoganglionosis in the gastric antrum and a decreased proportion of nNOS neurons as compared to younger mice (age 5-7 weeks). This was associated with a significant age-dependent decrease in liquid and solid gastric emptying. A novel model of gastric antrum hypoganglionosis was established using neural crest-specific expression of diphtheria toxin receptor. In this model, a significant reduction in liquid and solid gastric emptying is observed.

CONCLUSIONS & INFERENCES

Older mice exhibit delayed gastric emptying associated with hypoganglionosis and a reduction in nNOS-expressing neurons in the antrum. The causal relationship between antral hypoganglionosis and delayed gastric emptying was verified using a novel experimental model of ENS ablation. This study provides new information regarding the pathogenesis of delayed gastric emptying and provides a robust model system to study this disease and develop novel treatments.

Role of estrogen and stress on the brain-gut axis

Symptoms of functional gastrointestinal disorders (FGIDs), including fullness, bloating, abdominal pain, and altered gastrointestinal (GI) motility, present a significant clinical problem, with a reported prevalence of 25%-40% within the general population. More than 60% of those affected seek and require healthcare, and affected individuals report a significantly decreased quality of life. FGIDs are highly correlated with episodes of acute and chronic stress and are increased in prevalence and reported severity in women compared with men. Although there is evidence that sex and stress interact to exacerbate FGID symptoms, the physiological mechanisms that mediate these sex-dependent disparities are incompletely understood, although hormonal-related differences in GI motility and visceral sensitivity have been purported to play a significant role in the etiology. In this mini review, we will discuss brain-gut axis control of GI motility and sensitivity, the influence of estrogen on GI motility and sensitivity, and stress modulation of the brain-gut axis.

Changes in Gastric Smooth Muscle Cell Contraction during Pregnancy: Effect of Estrogen

It is well known that pregnancy is associated with frequent gastrointestinal (GI) disorders and symptoms. Moreover, previous reports have shown that estrogen, which changes in levels during pregnancy, participates in the regulation of GI motility and is involved in the pathogenesis of various functional disorders in the stomach. The aim of the current study was to explore the changes in the expression of estrogen receptors (ERs) and examine the effect of estrogen on nitric oxide- (NO-) cyclic guanosine monophosphate (cGMP) pathway and thus relaxation in gastric smooth muscle cells (GSMC) during pregnancy. Single GSMC from early-pregnant and late-pregnant Sprague-Dawley rats were used. Protein and mRNA expression levels of ERs were measured via specifically designed enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR), respectively. NO and cGMP levels were measured via specifically designed ELISA kits. Effect of estrogen on acetylcholine- (ACh-) induced contraction of single GSMC was measured via scanning micrometry in the presence or absence of the NO synthase inhibitor, N-nitro-L-arginine (L-NNA), or guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ). Estrogen increased both NO and cGMP levels and their levels were greater in early compared to late pregnancy. Expression of ERs was greater in early compared to late pregnancy. ACh induced greater contraction of GSMC in late pregnancy compared to early pregnancy. Estrogen inhibited ACh-induced contraction in both periods of pregnancy. Importantly, pretreatment of GSMC with either L-NNA or ODQ abolished estrogen inhibitory action on muscle contraction. In conclusion, GSMC contractile behavior undergoes drastic changes in response to estrogen during pregnancy and this might explain some of the pregnancy-associated gastric disorders.

Effect of progesterone on nitric oxide/cyclic guanosine monophosphate signaling and contraction in gastric smooth muscle cells

Previous studies have shown that progesterone could inhibit muscle contraction in various sites of the gastrointestinal tract. The underlying mechanisms responsible for these inhibitory effects of progesterone are not fully known. The aim of the current study was to investigate the effect of progesterone on the nitric oxide (NO)/cyclic guanosine monophosphate (cGMP) pathway and muscle contraction in the stomach. Single gastric smooth muscle cells from female Sprague-Dawley rats were used. The expression of progesterone receptor (PR) mRNA was analyzed by reverse transcription polymerase chain reaction. NO and cGMP levels were measured via specific ELISAs. Acetylcholine (ACh)-induced contraction of single gastric muscle cells preincubated with progesterone was measured via scanning micrometry in the presence or absence of the NO synthase inhibitor, Nω-Nitro-L-arginine (L-NNA), or guanylyl cyclase inhibitor, 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), and expressed as percent shortening from resting cell length. PR expression was detected in the stomach muscle cells. Progesterone inhibited ACh-induced gastric muscle cell contraction. Furthermore, progesterone increased NO and cGMP levels in single gastric muscle cells. Most notably, pre-incubation of muscle cells with either L-NNA or ODQ abolished the inhibitory action of progesterone on muscle contraction. These present observations suggest that progesterone promotes muscle cell relaxation in the stomach potentially via the NO/cGMP pathway.